The most common image is the trial version, but I believe the Chassuer Ardennes actually purchased the fifty vehicles of the C model. I could find little or no record of how many were built of each type, it seems several different were in production at the same time, all seemed to have the pivot in the chassis though. The Belgian vehicle document mentions 50 ordered and 35 Alvis Hefty tractors purchased for Chassuer Ardennes for artillery tows unknown if they were all delivered though, as of yet I have found no pictures of the vehicle in service are available.
A early model referred to as the mountain model, could not find much information about this model at all.
Not sure if this is the army model that was sold to the Belgians, but it looks like the Hefty B
Production model, this is the one I will scratch build I think the Alvis Hefty C
Hefty type B Used by the RAF 54 in service (cannot find any more details or more pictures of it though)
I am waiting of a Belgian produced artillery book to arrive to look at the images in it, before I dive into the scratch building of this beast.